The present invention relates to the transmitting and receiving system and device of a communication system, which uses a code division multiple access (referred to as CDMA, hereinafter) communication system for transmitting an information signal after modulating the same by a signal having a speed several tens to several hundreds times as fast as its speed.
As a prior art for such a system, for example, a miniaturized device was disclosed in JP-A-132934/1990. This device is constructed in such a manner that in an identification signal transmitter for transmitting an identification signal containing a frame synchronizing signal and an error detecting code and data containing a frame synchronizing signal and an error detecting code, an inverter and a switch are provided for making frame synchronizing signals completely different from each other between identification signal transmission and data transmission.
This conventional identification signal transmitter will now be described by referring to FIG. 4. As shown in FIG. 4, the conventional identification signal transmitter includes an identification code storage circuit 401, a frame synchronizing signal generating circuit 402, an inverter 403, first and second switches 404 and 405, an error detection encoder 406 and a sequential circuit 407.
Next, the operation of the conventional identification signal transmitter will be described.
The identification code storage circuit 401 outputs an identification signal to the second switch 405, described later. The frame synchronizing signal generating circuit 402 directly outputs a frame synchronizing signal to the first switch 404. Alternatively, the circuit 402 outputs a frame synchronizing signal to the first switch 404 after inverting its polarity by the inverter 403. During transmission of an identification signal, this first switch 404 selects a non-inverted frame synchronizing signal which has not been passed through the inverter 403. During transmission of data, however, the switch 404 selects and outputs an inverted frame synchronizing signal which has been passed through the inverter 403.
The second switch 405 operated associatively with the first switch 404 switches identification signals from the identification code storage circuit 401 with data and then outputs the results to the error detection encoder 406. The signals having been passed through the error detection encoder 406 are output from the sequential circuit 407 in sequence according to a transmission signal format.
With the above-described conventional identification signal transmitter, since frame synchronizing signals are made completely different from each other between transmission of an identification signal and transmission of data by using the inverter 403, a communication system which can prevent misunderstanding between data and an identification signal in a receiving side is provided.
Referring to JP-A-174841/1986, there is disclosed an art for capturing synchronization of a spread spectrum without using any delay lock loops in a receiver side. According to this application, in order to simplify synchronizing timing in the receiver side, the spread spectrum system of a frequency hopping coherent detection system is constructed in such a manner that a dual scrambler for a hopping pattern and a signal itself is used, and the same bit is used for a signal for capturing the hopping pattern and a frame synchronizing signal for scrambling of a signal frame unit. In other words, a transmission signal is scrambled by the serial pseudo noise (referred to as PN, hereinafter) signal of a 10th-order group. But since first 16 bits of the frame are synchronizing signals, these signals are not subjected to scrambling and become particular synchronizing patterns. For a carrier having been subjected to frequency hopping, a PN signal of 7th-order signal was used for the frequency hopping. But in a time portion equivalent to the first 16 bits of the above-noted frame, no frequency hopping is performed. In the receiver side, detection of a receiving timing is performed by detecting such particular synchronizing patterns which are known beforehand by a matched filter.
With this conventional spread spectrum system, there exists a capturing pattern not spread in the hopping pattern, this pattern is not subjected to scrambling for a signal and a synchronizing pattern is also provided for processing of a signal by a frame unit. Accordingly, a communication system is realized, whereby frequency hopping and frame synchronization are simultaneously performed only by simple pattern matching in the receiver side.
Conventionally, in the case of the communication system which communicates information by using the spread spectrum, especially if a single user type interference canceller is used, the interference canceller estimates the distortion of a signal in a transmission line only by a code allocated to the canceller without knowing spreading codes allocated to the other users. In this case, it may happen that the interference canceller makes a mistake in the estimation of a transmission line and misunderstands other user's signals for its own.
In order to avoid this problem and easily determine whether a signal pulled in by the interference canceller is a signal for its own use or not, in the above-noted communication system, a transmitted and received signal must contain information specific to each user.
In connection with this problem, the prior art disclosed in JP-A-132934/1990 is disadvantageous in that the generation of frame synchronizing signals increases the size of a circuit. This is specifically because it is difficult to provide new identification signals for quite a number of users by using only; an inverter and a switch. Even if a device for each user is individually provided and all kinds of identification signals are provided, a great increase inevitably occurs in the size of the circuit.
The prior art disclosed in JP-A-174841/1986 is also disadvantageous in that it is impossible to multiplex a plurality of users. This is because the original purpose of the spread spectrum communication system is to multiplex plural bits of information on the same time and on the same frequency by spreading information signals with codes. In the case of this prior art, the use of a common timing capturing signal for scrambling of an information signal and hopping of a communication frequency is effective for a reduction in the size of the circuit. However, since the signal for timing capture is not subjected to scrambling or frequency hopping, this portion cannot be multiplexed when a plurality of users are to be multiplexed.